According to a conventional technique, communication between a server and a client is performed using a common key encryption method. For example, according to another technique, in a client-server system, a client and a server each retain a key storing unit to store predetermined common keys whose generations differ from each other, and execute communication using one common key among the predetermined common keys.
According to another related technique, for example, in communication between an on-vehicle device in a vehicle and a server, a portable apparatus is used to authenticate the qualification to rewrite information of the on-vehicle device. According to yet another technique, a communicating state is migrated from an information communication apparatus using a telephone line network or an Internet protocol (IP) communication network, to an on-vehicle device, or the communicating state is migrated from the on-vehicle device to the information communication apparatus.
According to another technique, a common key encryption method is used between a server and a communications terminal, and between the communications terminal and an apparatus to be controlled. According to yet another technique, a server and a communications terminal execute communication using a common key; when a connection request is issued from the communications terminal and it is confirmed that the communications terminal does not retain any common key, the server transmits a common key to the communications terminal. According to another disclosed technique, when a common key for data is updated between a server and a communications terminal, the common key after the updating is encrypted using the common key before the updating and is transmitted to the communications terminal (see, e.g., Japanese Laid-Open Patent Publication Nos. 2003-174444; 2008-59450: 2009-267562; 2001-249899; 2003-244123; and 2008-67074.)